What causes mental illness?

If you think determining how genetics affects mental health is fraught, trying to figure out how nongenetic factors could lead to mental disorders can throw you for an even bigger loop.

How far back in a person's life do we look for an environmental trigger? How do we safeguard against ignoring a less catastrophic event (an allergy), and singling out only events we find compelling (the use of psychotropic drugs)? How can we determine if a genetic component interacts with an environmental one?

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The latter scenario is probably the trickiest but also extremely likely. Most mental health experts believe that a combination of genetic factors and exposure to environmental factors cause mental illness. It's multifactorial. And schizophrenia is back to bolster that claim.

A study by the Swiss Federal Institute of Technology found some rather startling news about how environmental factors might contribute to a schizophrenic mind -- and when those factors might be most poised to come into play. Using mice that were specially bred to complete a life cycle at a faster rate, they found that a viral infection or influenza during the first stages of a mother's pregnancy, combined with exposure to major stress during puberty, increased the likelihood of the mice developing schizophrenic-like brain functioning [source: Rüegg]. Now don't get too alarmed; researchers pointed out that it's not uncommon for mothers to get infections in pregnancy. Nor should you throw in the towel if you had a stressful middle school experience. Since only 1 percent of the population is schizophrenic, the flu and bullying does not a schizophrenic make.

We also know that brain chemistry must play a part in mental illness, because we know that giving people medication that addresses brain chemistry often works to regulate or resolve the disorder. But observing brain biochemistry isn't an easy process; you can't exactly crack open a person's head and ask them to say "ahh." What we do know is that our brain cells (or neurons) are excited or inhibited by neurotransmitters. And if we have abnormal amounts (large or small) of these neurotransmitters, we might observe a marked deviation in behavior or mood.

So there you have it: We don't know the exact causes of mental illness, but we have some really compelling cases for several factors.